1. Field of the Invention
The present invention relates to a method of manufacturing glued laminated wood which is made of wood sheets such as veneer sheets provided by rotary peeling, slicing, or other wood material as obtained by sawing or otherwise prepared. More specifically, it relates to a method of laying such wood sheets and laminating them together successively by means of thermosetting adhesive thereby to produce the glued laminated wood in the form of a multiple-layered board or a billet with a desired thickness and length.
2. Description of the Related Art
For better understanding of the underlying background of the present invention, firstly reference is made to FIG. 73 which schematically shows a prior art apparatus for making laminated veneer lumber (LVL) wherein veneer sheets are laminated together the end joints thereof disposed in a staggered array and with the wood grain of each veneer sheet running primarily along the length of the resulting product or LVL board.
The apparatus includes three sets of hot presses X, Y and Z arranged at three different stages spaced at an interval along the direction in which the LVL board is conveyed as indicated by arrow at the right-hand side on the drawing. Each of the hot presses X, Y and Z has a pair of movable upper and lower heat plates X1, Y1 and Z1 disposed one above the other, respectively. For the sake of the description of the apparatus, these three sets of hot presses X, Y and Z will be referred to as the first, second and third hot presses, respectively. Though not shown specifically in the drawing, there are provided three sets of veneer feeders associated with the respective hot presses X, Y and Z, and each set includes upper and lower movable veneer sheet feeders as indicated by arrows which depict the feeding directions. In the drawing, reference symbols A, B and C designate veneer sheets each having substantially the same length, width and thickness and disposed in the same orientation with the wood grain thereof extending substantially parallel to each other, i.e. extending along the lengthwise direction of the LVL board. It is noted that, for the sake of convenience in illustration, each veneer sheet is illustrated with a thickness which is shown exaggeratedly large relative to its length and also that a conveyer for moving a work in process is omitted from the illustration.
In manufacturing the LVL board with the apparatus of FIG. 73, firstly a pair of veneer sheets A depicted by shading is prepared with one surface of either one of such veneer sheets A coated with thermosetting adhesive. These veneer sheets A are fed by the first feeders for the first hot press X and combined in contact with each other with the adhesive-coated surface placed between the mating surfaces of the two veneer sheets A and with the ends thereof in an offset or staggered relation as shown in the drawing. These two veneer sheets A thus placed one on the other are conveyed to the first pressing station between the first heat plates X1, where the veneer sheets A are glued together under heat and pressure by the hot press X. After the first hot pressing operation is competed and the heat plates X1 are retracted, the glued laminated veneer sheets A are conveyed toward the second pressing station at the second hot press Y. On the way to the second pressing station, i.e. at an appropriate position between the first and second pressing stations, another pair of veneer sheets B, indicated by shading, each having on the inner surfaces thereof coated with adhesive is fed by the second veneer sheet feeders and laid on the opposite outer surfaces of the previously laminated veneer sheets A in a staggered relation to the veneer sheets A. The veneer sheets B thus laid onto the veneer sheets A are conveyed therewith to the second pressing station, where the veneer sheets B are pressed by the second hot press Y to be bonded to the laminated veneer sheets A.
After pressing by the second hot press Y is over, the laminated veneer sheets A and B are conveyed toward the third station at the third hot press Z. At an appropriate position between the second and third pressing stations, still another pair of veneer sheets C, indicated by shading, having on the inner surfaces thereof coated with adhesive is fed by the third veneer feeders and laid on the opposite outer surfaces of the veneer sheets B in a staggered arrangment. The veneer sheets C thus placed on the laminated veneer sheets A and B are conveyed to the third pressing station, where they are similarly pressed by the third hot press Z. Thus, an assembly of laminated veneer sheets A, B and C is formed.
Steps of operation including the above veneer sheet feeding, laying, hot pressing and conveying are performed successively at the respective positions and stations, whereby an LVL board with six plies as counted through its thickness is formed in a manner which is well known to those skilled in the art. As shown in FIG. 73, any two adjacent veneer sheets A, B or C in each layer are disposed with the ends thereof abutting closely each other to form end joints, and the veneer sheets A, B and C are laid such that the end joints are distributed in a regularly staggered arrangement in the resulting LVL board. As is apparent to those skilled in the art, if end joints in any two adjacent layers are located in alignment with each other across the thickness of the board, stress tends to be centered at such joints when the board is subjected to bending force, thereby inviting breakage of the board. Therefore, the purpose of the staggered arrangement of the end joints of the component veneer sheets is to avoid such concentration of stress at specific locations in the board.
For successful gluing of veneer sheets with the desired bonding strength, heat and pressure by hot pressing should be applied uniformly to the entire surfaces of veneer sheets with at least one of the mating surfaces thereof coated with adhesive. In hot pressing a pair of veneer sheets A, B or C in an offset or staggered arrangement as shown in FIG. 73 in the above apparatus, however, part of the paired combined veneer sheets fails to receive direct hot pressing action by the hot press. That is, upstream end portions of veneer sheets A, B and C, as viewed in the conveying direction, which are indicated by R, fail to be pressed directly by the hot press, although some heat will be conducted to such area of the veneer sheets. As a result, the upstream end portions of veneer sheets will not be bonded with the desired strength, thus affecting the quality of the resulting product.
If veneer sheets are laid in such a staggered array that the area R is narrowed with an attempt to obviate the above drawback, the end joints in any two adjacent layers in the board will be disposed closer to each other, thereby rendering the board weaker against bending.
Therefore, it is an object of the present invention to provide a method of manufacturing glued laminated wood which can solve the above-described problems. More specifically, an object of the invention is to provide a method which can hot press the entire surface of wood sheets such as veneer sheet for production of glued laminated wood with the desired strength and quality.